It is known that stable cupric hydroxide cannot be produced directly by a reaction between ordinary water-soluble copper salts, such as cupric sulfate, and sodium hydroxide. The reaction results in a gelatinous precipitate which is gradually transformed into black cupric oxide.
For this reason other methods of producing cupric hydroxide have been adopted, such as the treatment of scrap copper with injected air in a 3% solution of ammonia (U.S. Pat. No. 2,536,096) or the treatment of cupric nitrate solutions with concentrated sodium carbonate solution at 80.degree. C. (German Pat. No. 824,200). But the resulting products lack stability and tend to be transformed to cupric oxide.
In other known processes, cupric sulfate and trisodium phosphate in equimolar quantities are reacted to form copper-sodium phosphate (CuNaPO.sub.4) which is then transformed to cupric hydroxide after an addition of an adequate quantity of sodium hydroxide (U.S. Pat. Nos. 2,666,688 and Re 24,324).
The cupric hydroxides produced by the so-called "phosphate process" have the disadvantage that owing to the large number of variable parameters, such as temperature, quantitative proportions, concentration, pH value etc, the resulting cupric hydroxide varies widely in composition and properties. Another disadvantage of that process is that it produces byproduct sodium sulfate in a large quantity of 1 mole per mole of cupric hydroxide creating a disposal problem.
In a different process, in which electrolysis is employed, the solution of a copper salt formed from the copper anode is contacted in the cathode chamber with hydroxyl ions which are present or have been formed there. The electrolytic solution is a solution of sodium sulphate with an addition of sodium phosphate (Open German Application 15 92 441). That process is rather expensive because means for carrying out electrolysis are required.
In processes of a different kind, cupric hydroxide is produced from cupric oxychloride (3 Cu(OH).sub.2.CuCl.sub.2.XH.sub.2 O), in which the copper hydroxide has partly been preformed and which is reacted with basic substances, such as quicklime, at elevated temperatures (German Pat. No. 306,035) and, if desired, under superatmospheric pressure (German Pat. No. 272,182), and optionally with a further dissolution of the cupric hydroxide with ammonia water and renewed precipitation (German Pat. No. 461,556). But the resulting end products also lack adequate stability.